Users of certain types of electrical apparatus often have need of a device to register the accumulated running time of the apparatus, whether for warranty, preventive maintenance, billing purposes, energy audit or duty analysis. As an example, consider a user of irrigation water supplied from a well regulated by a state agency. The agency often assumes that the water will be pumped at a given rate throughout a certain season. This means that a person who uses less water than the assumed amount is charged for the full amount anyway, unless he can show that his actual consumption was less than the assumed amount.
One way to make such a showing is to include an hour meter into the circuit supplying power to the motor of the pump. While this is in principle easy to do, it may well require the services of an electrician, especially if local electrical codes are to be observed, or if the job involves multi-phase circuits, or involves particularly high voltage or particularly high currents which would give the average layman cause for technical concern. Electricians, however, can be expensive, as can be the supplies needed to properly carry out the task. It would be beneficial if there were a quick, easy and low cost way to equip a piece of equipment with an hour meter, without the need for making any electrical connections to the equipment.
One way this can sometimes be done is with a so-called "vibratory" hour meter, such as is produced by Grasslin firm in the Federal Republic of Germany, and available in the United States from at least Fargo Controls, Inc., of Eatontown, N.J. In this type of device the inherent mechanical vibration in the equipment is coupled to the hour meter (by attachment of the hour meter thereto) and made to power the hour meter. However, a certain minimum vibratory excursion is required, depending upon the frequency of the vibration. And while vibratory hour meters are commonly used on internal combustion engines and other reciprocating machinery, such as compressors, many types of electrical machinery simply run too smoothly to activate a vibratory hour meter.
Furthermore, it may not always be possible nor desirable to mount the hour meter directly onto the casing or housing of the motor or its load, even if there is sufficient vibration at such a location. Perhaps these are enclosed and behind seals or cannot be conveniently accessed on a regular basis appropriate for reading the hour meter. In such a case it would be desirable to have at hand an hour meter that could be attached either directly to the motor or, if need be, merely placed in appropriate proximity to the electrical conductors supplying power to the motor.